Proteomic changes in the gills of wild-type and transgenic radiosensitive medaka following exposure to direct irradiation and to X-ray induced bystander signals

Proteomic profile of epidermal mucus from Labeo rohita reveals differentially abundant proteins after Aeromonas hydrophila infection

We report the proteomic profile of Epidermal Mucus (EM) from Labeo rohita and identified the differentially abundant proteins (DAPs) against Aeromonas hydrophila infection through label-free liquid chromatography-mass spectrometry (LC-MS/MS). Using discovery-based proteomics, a total of 2039 proteins were quantified in nontreated group and 1,328 proteins in the treated group, of which 114 were identified as DAPs in both the groups. Of the 114 DAPs, 68 proteins were upregulated and 46 proteins were downregulated in the treated group compared to nontreated group. Functional annotations of these DAPs shows their association with metabolism, cellular process, molecular process, cytoskeletal, stress, and particularly immune system. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and Fisher's exact test between the two groups shows that most of the proteins were immune-related, which were significantly associated with the proteasome, phagosome, and Salmonella infection pathways. Overall, this study shows a basic and primary way for further functional research of the involvement of vitellogenin 2, alpha-2-macroglobulin-like protein, toll-like receptors (TLR-13), calpain, keratin-like proteins, and heat shock proteins against bacterial infection. Nonetheless, this first-ever comprehensive report of a proteomic sketch of EM from L. rohita after A. hydrophila infection provides systematic protein information to broadly understand the biological role of fish EM against bacterial infection.

Copper uptake in adult rainbow trout irradiated during early life stages and in non-irradiated bystander trout which swam with the irradiated fish

PURPOSE

This investigation forms part of a wider study into the legacy effects of exposure of rainbow trout eggs 38 h after fertilization, eyed eggs, yolk sac larvae (YSL) or first feeders to a single 0.5 Gy X-ray dose, including the induction of a bystander effect, by the irradiated fish, to non-irradiated fish. Fish may be exposed to multiple environmental stressors, including waterborne metals, during their lifespan and, while there are data on how the legacy of early life stage irradiation and bystander effect induction is affected by waterborne aluminum and cadmium, there are no studies into the effects radiation or the radiation induced bystander effect on metal uptake. Therefore the aim of this investigation was to determine if the legacy of early life stage irradiation included an effect on copper uptake by adult fish and by non-irradiated bystander adult trout which swam with the irradiated fish.

METHODS

The four early life stages mentioned above were exposed to a single 0.5 Gy X-ray dose and then maintained, for two years with no further irradiation. At two years old the irradiated fish were allowed to swim, for 2 h with non-irradiated bystander trout (also two years old). After this time copper uptake was determined using ⁶⁴Cu.

RESULTS

Copper uptake was increased in adult trout irradiated as eggs at 48 h after fertilization and as first feeders but eyed egg or YSL irradiation had no effect. Copper uptake was also increased in the bystander trout which swam with trout irradiated as eggs at 48 h after fertilization and as eyed eggs but there was no effect on non-irradiated adult trout which swam with trout irradiated as YSL or first feeders.

CONCLUSIONS

When put in context with the proteomic changes observed in these fish we propose the increased copper uptake in adult trout irradiated as eggs at 48 h after fertilization could be part of an anti-tumorigenic response and the increase in copper uptake in adult trout irradiated as first feeders could be part of a potentially protective pro-apoptotic response. Similarly we propose the increase in copper uptake in non-irradiated adult trout, induced by trout irradiated as eggs at 48 h after fertilization or as eyed eggs, was part of the universally anti-tumorigenic nature of the X-ray induced bystander effect in fish. However this was exclusive to embryonic irradiation.

Effects of chronic exposure to low levels of IR on Medaka (Oryzias latipes): a proteomic and bioinformatic approach

PURPOSE

Chronic exposure to ionizing radiation (IR) at low doses (<100 mGy) has been insufficiently studied to understand fully the risk to health. Relatively little knowledge exists regarding how species and healthy tissues respond at the protein level to chronic exposure to low doses of IR, and mass spectrometric-based profiling of protein expression is a powerful tool for studying changes in protein abundance.

MATERIALS AND METHODS

SDS gel electrophoresis, LC-MS/MS mass spectrometry-based approaches and bioinformatic data analytics were used to detect proteomic changes following chronic exposure to moderate/low doses of radiation in adults and normally developed Medaka fish (Oryzias latipes).

RESULTS

Significant variations in the abundance of proteins involved in thyroid hormone signaling and lipid metabolism were detected, which could be related to the gonadal regression phenotype observed after 21.04 mGy and 204.3 mGy/day exposure. The global proteomic change was towards overexpression of proteins in muscle and skin, while the opposite effect was observed in internal organs.

CONCLUSION

The present study provides information on the impacts of biologically relevant low doses of IR, which will be useful in future research for the identification of potential biomarkers of IR exposure and allow for a better assessment of radiation biosafety regulations.

Elke Bräuer-Krisch: dedication, creativity and generosity: May 17, 1961-September 10, 2018

PURPOSE

This extraordinary woman worked her professional way from a radiation protection engineer to become the successful principal investigator of a prestigious international European project for a new radiation therapy (ERC Synergy grant, HORIZON 2020). The evaluation of the submitted proposal was very positive. The panel proposed that it be funded. Elke tragically passed away a few days before this conclusion of the panel. The present account describes her gradual career development; it includes many episodes that Elke personally chronicled in her curriculum of 2017.

METHODS

An internet literature search was performed using Google Scholar and other sources to assist in the writing of this narrative review and account.

CONCLUSIONS

In parallel to the development of the new Biomedical Beamline ID17 at the European Synchrotron Radiation Facility in Grenoble in the late nineties, Elke focused her interest and her personal and professional priorities on MRT, particularly on its clinical goals. She outlined her main objectives in several documents: (1) develop a new paradigm of cancer care by broadening the foundation for MRT. (2) Filling the gaps in basic biological knowledge about the mechanisms of MRT effects on normal and neoplastic tissues. (3) Broaden the preclinical level of evidence for the low normal organ toxicity of MRT versus standard X-ray irradiations; preclinical experiments involved the application of MRT to animal tumor patients, to animals of larger size than laboratory rodents, using larger radiation field sizes, and irradiating in a real-time scenario comparable to the one planned for human patients. (4) To foster the specific purpose of radiosurgical MRT of tumor patients at the ESRF that required development of new, specific state of the art modalities and tools for treatment planning, dosimetry, dose calculation, patient positioning and, of particular importance, redundant levels of patient safety. Just as she was about to take responsibility as principal investigator for a prestigious international European project on a new radiation therapy, death called Elke in.

An Effective Protocol for Proteome Analysis of Medaka (Oryzias latipes) after Acute Exposure to Ionizing Radiation

All terrestrial organisms are subject to evolutionary pressures associated with natural sources of ionizing radiation (IR). The legacy of human-induced IR associated with energy, weapons production, medicine, and research has changed the distribution and magnitude of these evolutionary pressures. To date, no study has systematically examined the effects of environmentally relevant doses of radiation exposure across an organismal proteome. This void in knowledge has been due, in part, to technological deficiencies that have hampered quantifiable environmentally relevant IR doses and sensitive detection of proteomic responses. Here, we describe a protocol that addresses both needs, combining quantifiable IR delivery with a reliable method to yield proteomic comparisons of control and irradiated Medaka fish. Exposures were conducted at the Savannah River Ecology Laboratory (SREL, in Aiken, SC), where fish were subsequently dissected into three tissue sets (carcasses, organs and intestines) and frozen until analysis. Tissue proteins were extracted, resolved by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE), and each sample lane was divided into ten equal portions. Following in-gel tryptic digestion, peptides released from each gel portion were identified and quantified by Liquid Chromatography-Mass Spectrometry (LC-MS/MS) to obtain the most complete, comparative study to date of proteomic responses to environmentally relevant doses of IR. This method provides a simple approach for use in ongoing epidemiologic studies of chronic exposure to environmentally relevant levels of IR and should also serve well in physiological, developmental, and toxicological studies.

Irradiation of rainbow trout at early life stages results in a proteomic legacy in adult gills. Part A; proteomic responses in the irradiated fish and in non-irradiated bystander fish

Exposure to a single 0.5 Gy X-ray dose of eggs at 48 h after fertilisation (48 h egg), eyed eggs, yolk sac larvae (YSL) and first feeders induces a legacy effect in adult rainbow trout. This includes the transmission of a bystander effect to non-irradiated adult trout which had swam with the irradiated fish. The aim of this study was to investigate this legacy by analysing the gill proteome of these irradiated and bystander fish. Irradiation at all of the early life stages resulted in changes to proteins which play a key role in development but are also known to be anti-tumorigenic and anti-oxidant: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin, serum albumin 1 precursor (eyed eggs), clathrin heavy chain 1 isoform X10 (eyed eggs and first feeders), and actin-related protein 2/3 complex subunit 4 (first feeders), downregulation of pyruvate dehydrogenase, histone 1 (48 h egg), triosephosphate isomerase (TPI), collagen alpha-1(1) chain like proteins (YSL), pyruvate kinase PKM-like protein (YSL and first feeders), ubiquitin-40S ribosomal proteins S27 and eukaryotic translation initiation factor 4 A isoform 1B (first feeders). However irradiation of YSL and first feeders (post hatching early life stages) also induced proteomic changes which have a complex relationship with tumorigenesis or cancer progression; downregulation of alpha-1-antiprotease-like protein precursor, vigilin isoform X2 and nucleoside diphosphate kinase (YSL) and upregulation of hyperosmotic glycine rich protein (first feeders). In bystander fish some proteomic changes were similar to those induced by irradiation: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin (eyed eggs), actin-related protein 2/3 complex subunit 4, hyperosmotic glycine rich protein (first feeders), and downregulation of alpha-1-antiprotease-like protein, vigilin isoform X2, nucleoside diphosphate kinase (YSL), pyruvate kinase PKM-like protein and ubiquitin-40S ribosomal protein S27a-like (first feeders). Other proteomic changes were unique to bystander fish; downregulation of TPI, ubiquitin-40S ribosomal protein S2 (eyed egg), cofilin-2, cold-inducible RNA-binding protein B-like isoform X3 (YSL) and superoxide dismutase (first feeder), and upregulation of haemoglobin subunit alpha, collagen 1a1 precursor, apolipoprotein A-1-1 and A-1-2 precursor (first feeders). These bystander effect proteomic changes have been shown to be overwhelmingly anti-tumorigenic or protective of the fish gill.

Irradiation of rainbow trout at early life stages results in a proteomic legacy in adult gills. Part B; the effect of a second radiation dose, after one year, on the proteomic responses in the irradiated and non-irradiated bystander fish

This study extends the investigation of the legacy effects of exposure to a single radiation dose at one of four early life stages, in adult rainbow trout (Part A), by examining the effects of a second identical dose after one year; i.e. egg 48 h after fertilisation (48 h egg) + 1 year, eyed egg + 1 year, yolk sac larvae (YSL) + 1 year and first feeder + 1 year. This included the induction of a bystander effect in non-irradiated trout which had swam with the irradiated fish. The second radiation dose negated any beneficial proteomic responses following early life stage irradiation only, particularly irradiation of 48 h eggs and eyed eggs (Part A). Instead the responses after early life stage + 1 year irradiation are consistently associated with tumorigenesis, cancer progression, or are otherwise damaging: upregulation of alpha-globin 1 (YSL + 1 year and first feeders + 1 year) and downregulation of histone H1, type II keratin, malate dehydrogenase 2-2, Na/K ATPase alpha subunit isoform 1b, nucleoside diphosphate kinase (48 h egg + 1 year), electron transfer flavoprotein subunit alpha (eyed egg + 1 year), 60 S ribosomal protein L30 (YSL + 1 year) and haemoglobin subunit beta-4 (first feeder + 1 year). Most significantly the second radiation dose also negated the overwhelmingly beneficial bystander effect proteomic responses induced by trout irradiated at an early life stage only (Part A). Instead the bystander effect proteomic changes induced by trout irradiated at an early life stage and again at 1 year have been associated with uncertain, with respect to tumorigenesis, or detrimental effects; upregulation of alpha-globin 1 (YSL + 1 year and first feeder + 1 year) and downregulation of malate dehydrogenase 2-2, nucleoside diphosphate kinase (48 h egg + 1 year), transferrin precursor (eyed egg + 1 year), 60 S ribosomal protein L30 (YSL + 1 year) and serine / threonine-protein phosphatase 2 A 65 kDa (first feeder + 1 year). This difference between the bystander effect induced proteomic changes following early life stage irradiation only and early life stage + 1 year irradiation may indicate a fundamental change in the non-targeted effects of radiation following multiple exposure to radiation.

Homogenous and Microbeam X-Ray Radiation Induces Proteomic Changes in the Brains of Irradiated Rats and in the Brains of Nonirradiated Cage Mate Rats

To evaluate microbeam radiation therapy (MRT), for brain tumor treatment, the bystander effect in nonirradiated companion animals was investigated. Adult rats were irradiated with 35 or 350 Gy at the European Synchrotron Research Facility using homogenous irradiation (HR) or MRT to the right brain hemisphere. The irradiated rats were housed with nonirradiated rats. After 48 hours, all rats were euthanized and the frontal lobe proteome was analyzed using 2-dimensional electrophoresis and mass spectrometry. Proteome changes were determined by analysis of variance (P < .05). Homogenous irradiation increased serum albumin, heat shock protein 71 (HSP-71), triosephosphate isomerase (TPI), fructose bisphosphate aldolase (FBA), and prohibitin and decreased dihydrolipoyl dehydrogenase (DLD) and pyruvate kinase. Microbeam radiation therapy increased HSP-71, FBA, and prohibitin, and decreased aconitase, dihydropyrimidinase, TPI, tubulin DLD, and pyruvate kinase. Cage mates with HR irradiated rats showed increased HSP-71 and FBA and decreased pyruvate kinase, DLD, and aconitase. Cage mates with MRT irradiated rats showed increased HSP-71, prohibitin, and FBA and decreased aconitase and DLD. Homogenous irradiation proteome changes indicated tumorigenesis, while MRT proteome changes indicated an oxidative stress response. The bystander effect of proteome changes appeared antitumorigenic and inducing radioresistance. This investigation also supports the need for research into prohibitin interaction with HSP-70/71 chaperones and cancer therapy.

Biological Entanglement-Like Effect After Communication of Fish Prior to X-Ray Exposure

The phenomenon by which irradiated organisms including cells in vitro communicate with unirradiated neighbors is well established in biology as the radiation-induced bystander effect (RIBE). Generally, the purpose of this communication is thought to be protective and adaptive, reflecting a highly conserved evolutionary mechanism enabling rapid adjustment to stressors in the environment. Stressors known to induce the effect were recently shown to include chemicals and even pathological agents. The mechanism is unknown but our group has evidence that physical signals such as biophotons acting on cellular photoreceptors may be implicated. This raises the question of whether quantum biological processes may occur as have been demonstrated in plant photosynthesis. To test this hypothesis, we decided to see whether any form of entanglement was operational in the system. Fish from 2 completely separate locations were allowed to meet for 2 hours either before or after which fish from 1 location only (group A fish) were irradiated. The results confirm RIBE signal production in both skin and gill of fish, meeting both before and after irradiation of group A fish. The proteomic analysis revealed that direct irradiation resulted in pro-tumorigenic proteomic responses in rainbow trout. However, communication from these irradiated fish, both before and after they had been exposed to a 0.5 Gy X-ray dose, resulted in largely beneficial proteomic responses in completely nonirradiated trout. The results suggest that some form of anticipation of a stressor may occur leading to a preconditioning effect or temporally displaced awareness after the fish become entangled.

Radiation-induced non-targeted effects: some open questions

The existence of non-targeted effects (NTEs) of radiation (genomic instability and bystander effects) has been generally accepted for >20 y; however, there is research, which was largely ignored going back to 1915 reporting these effects. Despite today's general acceptance of the phenomenon of NTE, there is little agreement about the mechanisms involved and the implications in radiation biology and radiation protection. The aim of this review was to consider some of the odd data, which have been published in the field with a view to obtaining insights or stimulating new ways of thinking about this field. By highlighting some key challenges and controversies, concerning the mechanisms and more importantly, the reason these effects exist, current ideas about the wider implications of NTEs in evolution and biology are also discussed.

Identification of Key Proteins in Human Epithelial Cells Responding to Bystander Signals From Irradiated Trout Skin

Radiation-induced bystander signaling has been found to occur in live rainbow trout fish (Oncorhynchus mykiss). This article reports identification of key proteomic changes in a bystander reporter cell line (HaCaT) grown in low-dose irradiated tissue-conditioned media (ITCM) from rainbow trout fish. In vitro explant cultures were generated from the skin of fish previously exposed to low doses (0.1 and 0.5 Gy) of X-ray radiation in vivo. The ITCM was harvested from all donor explant cultures and placed on recipient HaCaT cells to observe any change in protein expression caused by the bystander signals. Proteomic methods using 2-dimensional (2D) gel electrophoresis and mass spectroscopy were employed to screen for novel proteins expressed. The proteomic changes measured in HaCaT cells receiving the ITCM revealed that exposure to 0.5 Gy induced an upregulation of annexin A2 and cingulin and a downregulation of Rho-GDI2, F-actin-capping protein subunit beta, microtubule-associated protein RP/EB family member, and 14-3-3 proteins. The 0.1 Gy dose also induced a downregulation of Rho-GDI2, hMMS19, F-actin-capping protein subunit beta, and microtubule-associated protein RP/EB family member proteins. The proteins reported may influence apoptotic signaling, as the results were suggestive of an induction of cell communication, repair mechanisms, and dysregulation of growth signals.

Proteomic overview and perspectives of the radiation-induced bystander effects

Radiation proteomics is a recent, promising and powerful tool to identify protein markers of direct and indirect consequences of ionizing radiation. The main challenges of modern radiobiology is to predict radio-sensitivity of patients and radio-resistance of tumor to be treated, but considerable evidences are now available regarding the significance of a bystander effect at low and high doses. This "radiation-induced bystander effect" (RIBE) is defined as the biological responses of non-irradiated cells that received signals from neighboring irradiated cells. Such intercellular signal is no more considered as a minor side-effect of radiotherapy in surrounding healthy tissue and its occurrence should be considered in adapting radiotherapy protocols, to limit the risk for radiation-induced secondary cancer. There is no consensus on a precise designation of RIBE, which involves a number of distinct signal-mediated effects within or outside the irradiated volume. Indeed, several cellular mechanisms were proposed, including the secretion of soluble factors by irradiated cells in the extracellular matrix, or the direct communication between irradiated and neighboring non-irradiated cells via gap junctions. This phenomenon is observed in a context of major local inflammation, linked with a global imbalance of oxidative metabolism which makes its analysis challenging using in vitro model systems. In this review article, the authors first define the radiation-induced bystander effect as a function of radiation type, in vitro analysis protocols, and cell type. In a second time, the authors present the current status of protein biomarkers and proteomic-based findings and discuss the capacities, limits and perspectives of such global approaches to explore these complex intercellular mechanisms.

Low doses of gamma-irradiation induce an early bystander effect in zebrafish cells which is sufficient to radioprotect cells

The term “bystander effect” is used to describe an effect in which cells that have not been exposed to radiation are affected by irradiated cells though various intracellular signaling mechanisms. In this study we analyzed the kinetics and mechanisms of bystander effect and radioadaptation in embryonic zebrafish cells (ZF4) exposed to chronic low dose of gamma rays. ZF4 cells were irradiated for 4 hours with total doses of gamma irradiation ranging from 0.01–0.1 Gy. In two experimental conditions, the transfer of irradiated cells or culture medium from irradiated cells results in the occurrence of DNA double strand breaks in non-irradiated cells (assessed by the number of γ-H2AX foci) that are repaired at 24 hours post-irradiation whatever the dose. At low total irradiation doses the bystander effect observed does not affect DNA repair mechanisms in targeted and bystander cells. An increase in global methylation of ZF4 cells was observed in irradiated cells and bystander cells compared to control cells. We observed that pre-irradiated cells which are then irradiated for a second time with the same doses contained significantly less γ-H2AX foci than in 24 h gamma-irradiated control cells. We also showed that bystander cells that have been in contact with the pre-irradiated cells and then irradiated alone present less γ-H2AX foci compared to the control cells. This radioadaptation effect is significantly more pronounced at the highest doses. To determine the factors involved in the early events of the bystander effect, we performed an extensive comparative proteomic study of the ZF4 secretomes upon irradiation. In the experimental conditions assayed here, we showed that the early events of bystander effect are probably not due to the secretion of specific proteins neither the oxidation of these secreted proteins. These results suggest that early bystander effect may be due probably to a combination of multiple factors.

iTRAQ analysis of gill proteins from the zebrafish (Danio rerio) infected with Aeromonas hydrophila

The gills are large mucosal surfaces and very important portals for pathogen entry in fish. The aim of this study was to determine the gill immune response at the protein levels, the differential proteomes of the zebrafish gill response to Aeromonas hydrophila infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1338 proteins were identified and classified into the categories primarily related to cellular process (15.36%), metabolic process (11.95%) and biological regulation (8.29%). Of these, 82 differentially expressed proteins were reliably quantified by iTRAQ analysis, 57 proteins were upregulated and 25 proteins were downregulated upon bacterial infection. Gene ontology (GO) enrichment analysis showed that approximately 33 (8.8%) of the differential proteins in gills were involved in the stress and immune responses. Several upregulated proteins were observed such as complement component 5, serpin peptidase inhibitor clade A member 7, annexin A3a, histone H4, glyceraldehyde 3-phosphate dehydrogenase, creatine kinase, and peroxiredoxin. These protein expression changes were further validated at the transcript level using microarray analysis. Moreover, complement and coagulation cascades, pathogenic Escherichia coli infection and phagosome were the significant pathways identified by KEGG enrichment analysis. This is first report on proteome of fish gills against A. hydrophila infection, which contribute to understanding the defense mechanisms of the gills in fish.

Chronic exposure by ingestion of environmentally relevant doses of (226)Ra leads to transient growth perturbations in fathead minnow (Pimephales promelas, Rafinesque, 1820)

PURPOSE

To assess the impact of environmentally relevant levels of ingested (226)Ra on a common freshwater fish species.

METHODS

Fathead minnow (Pimephales promelas, Rafinesque) were obtained at the first feeding stage and established on a commercial fish food diet containing (226)Ra in the activity range 10 mBq/g(-1), -10,000 mBq/g(-1). They remained on this diet for 24 months and were sampled invasively at 1,6,18 and 24 months to assess growth, biochemical indices and accumulated dose and non-invasively also at 12 and 15 months to assess growth.

RESULTS

Fish fed 10 and 100 mBq/g(-1) diet showed a small transitory deregulation of growth at 6 and 12 months. Fish fed higher activities showed less significant or insignificant effects. There was a trend at 18 months which was stronger at 24 months for the population distribution to change in all of the (226)Ra fed groups so that smaller fish were smaller and bigger fish were bigger than the controls. There were also significant differences in the ratios of protein:DNA at 24 months which were seen as a trend but were not significant at earlier time points.

CONCLUSIONS

Fish fed a radium diet for 2 years show a small and transitory growth dysregulation at 6 and 12 months. The effects predominate at the lower activities suggesting hormetic or homeostatic adjustments. There was no effect on growth of exposure to the high activities (226)Ra. This suggests that radium does not have a serious impact on the ecology of the system and the level of radium that would be transferred to humans is very low. The results may be important in the assessment of long-term environmental impacts of (226)Ra exposure.

Neutrons do not produce a bystander effect in zebrafish irradiated in vivo

PURPOSE

Neutron irradiations at the McMaster Tandetron Accelerator were performed to study direct and bystander effects of neutrons in a live organism.

METHODS

The neutrons were produced through (7)Li(p,n)(7)Be reaction. Although the gamma contamination of the neutron beam cannot be completely eliminated, it was designed to be as low as possible and remain below a threshold already established for bystander effects. Microdosimetric methods using a tissue-equivalent proportional counter have been used to measure the neutron and gamma doses for the cell irradiation. Previous data for a cell line exposed in vitro suggested that neutrons did not produce bystander effects at doses below 300 mGy. The current experiments sought to confirm this using a live whole organism (zebrafish) where tissue samples harvested 2 h after exposure were examined for direct evidence of apoptosis and tested for secretion of bystander factors using an established bioassay. Fish were either exposed directly to the beam or were allowed to swim with or in water previously occupied by irradiated fish.

RESULTS

Using the zebrafish model it was found that there was significant direct cell death seen both by apoptosis scores and clonogenic assay when the neutron dose was approximately 100 mGy. An equivalent dose of gamma rays produced a more toxic effect. It was further found that neutrons did not induce a bystander effect in fish receiving signals from irradiated fish.

CONCLUSION

The results confirm in vitro experiments which suggest neutrons do not induce bystander signaling. In fact they may suppress gamma induced signaling suggesting a possible intriguing new and as yet unclear mechanism.